This invention relates to the treatment of heavy oils or heavy oil fractions of high asphaltene content, in order to convert them to lighter fractions whose transport and treatment by usual refining processes is easier. Oils from coal hydrogenation may also be treated.
More particularly, the invention solves the problem of converting a viscous, non transportable, crude oil of high metals, sulfur and asphaltenes content and comprising more than 50% of constituents having a normal boiling point higher than 520.degree. C., to a stable, easily transportable hydrocarbon product, of low metals, sulfur and asphaltenes contents and having only a reduced content, for example less than 20% by weight, of constituents of normal boiling point higher than 520.degree. C.
The problem solved by the invention has been studied for a long time; the main difficulty to overcome is that of the deactivation of the catalysts by impurities, mainly metal impurities, from the treated charges. Thus, for example, Boscan or Cerro Negro crude oil may contain from 200 to 1000 ppm by weight or more of metals; these metals are mainly vanadium and nickel, together with variable proportions of iron and other metals.
The deactivation of hydrotreatment catalysts is illustrated by U.S. Pat. No. 4,017,380 having for object to cope with this difficulty by using a cyclic process; a catalytic hydrodesulfuration (HDS) unit (I) precedes a visbreaking (II) unit containing a deactivated HDS catalyst; as soon as the active hydrodesulfuration catalyst (I) has deactivated, the operations are reversed after replacement of catalyst (II) by fresh catalyst: the charge then passes over the active HDS catalyst (II) under HDS conditions, then over the inactive catalyst (I) under visbreaking conditions.
There is thus place on the market for a really continuous process wherein the hydrotreatment catalyst may be used over several weeks or several months without deactivation.